P20EE00 Nox Sensor and Coolant Leak... related?

[Ed_T]

@mmi : I understand you are a bit of an Oracle when it comes to this subject. Any advice?
@Niknak : I've seen you post previously about a link between coolant leaks and NOx sensors failing. Can you please share a bit more info of what the link is?
Anyone else have some good advice?

I've just bought a T6 2017 2.0 150bhp on Thursday. I'm booked into the main dealer tomorrow for some investigatory work and for an oil change service, but would like to get some knowledge ahead of this. It is coming up with the NOx sensor fault P20EE00 SCR NOx Catalyst Efficiency Below Threshold Bank 1 Catalyst 1 (AA pre-purchase inspection picked it up in a historic read plus EML came on for me after about 2 hours driving... I checked the code and cleared it later that night and it's not come back over the past day or so but I'm sure it will). I was driving on cruise control around 50-70 (in and out of motorway roadworks) which from what I've read seems to be common conditions for the EML to come on with this fault. I've also noticed that the coolant level was low (below minimum) so I suspect an unresolved slow leak. Last (full) service was 12k miles ago.

There is also a historic P20F00 code (reductant system performance bank 1), but AA guy said this was from a long time ago. There is a receipt for some VW main dealer work on the Ad Blue not registering back in February 2023 ('system has been adapted and recalibrated'). Ad blue range was about 1600 when I picked up the van. Drove it a couple of hundred miles home, range dropped accordingly and 'top up needed' light came on at 1500. I dropped into my local VW yesterday for a free top up using some paperwork that came with the van and range increased to 4k miles, so this all seems to be working as expected.

I'm waiting for a Carista to arrive today but do have a different OBD reader. I can see in there that is says ECU software version is 6168, which I think means it already has the right update (attached)??? I also noticed that the 'NOx sensor concentration bank 1 sensor 1 reading on my OBD was showing as 65535 even with the engine turned off, and again sat with the engine running for a few minutes on the driveway (max possible value?) (attached image). In the emission test section of the app it states 'not passed since DTC reset' against NOx/SCR Monitor (attached image). I will get the engine up to temperature later today and repeat the NOx sensor reading with a warm engine in case it is just related to engine temperature.

Thanks for any advice.

Ed

 

[mmi]

NOx sensor fault P20EE00 SCR NOx Catalyst Efficiency Below Threshold Bank 1 Catalyst 1

I would say it's a wrong assumption that it's a sensor fault. It's the sensor reporting higher NOx emissions than expected. Of course could be the sensor but a faulty sensor would manifest itself with a different code. AFAIK there is not a single failed sensor reported on the Forum, just a couple of replaced ones- not curing the P20EE issue.

I also noticed that the 'NOx sensor concentration bank 1 sensor 1 reading on my OBD was showing as 65535 even with the engine turned off, and again sat with the engine running for a few minutes on the driveway (max possible value?) (attached image)

65535 (hex FFFF) is more just a "sensor not ready" indication. It will come to life when warmed up - takes some 10-20 minutes to reach operating temperature. Your engine doesn't have sensor 2, so that channel will stay silent. Some fancy details here:

Adblue /software version

As I see it my next plan of attack will be check the adblue injector is functioning and check adblue in the tank with refractometer does that sound about right ? Agreed, sounds like a plan :thumbsup:

www.t6forum.com

I checked the code and cleared it later that night

In the emission test section of the app it states 'not passed since DTC reset' against NOx/SCR Monitor (attached image).

Indeed, clearing engine faults also clears emission readiness statuses to "not passed". It can take some time to get them all passed - mine typically needs 250 km for the last one to "pass" (depends on number of ignition cycles, hot enough runs, etc.)

I can see in there that is says ECU software version is 6168, which I think means it already has the right update (attached)???

I've just bought a T6 2017 2.0 150bhp on Thursday

Correct, that's the up to date software identifier. However, I have observed that in the UK it's fairly popular to tinker with ECU softwares so perhaps would be beneficial to doublecheck it's really OEM software. In your attachment there is some verification information but can't confirm if they are the OEM ones.

Calibration Verification Numbers: 01E7FCF980
Calibration ID: 04L056KG6168JEAJ

Bonus threads:​

Below some measurements how the updated software should behave re NOx emissions.

[T6_measured] NOx emissions, AdBlue consumption, DPF regeneration - Before and after ECU update

Introduction An update campaign for T6 EU6 diesel engines took place in 2019-20. Affected engines were on van of model years MY16-MY18, including some of MY19. For M1 class (passenger carriers, VIN WV2...) the update was an official recall. For N1 class (VIN WV1....) the update was not...

www.t6forum.com

In case using Android perhaps something interesting for your Carista dongle - even NOx realtime monitoring.

[T6_measured] Monitoring DPF regeneration, DPF condition, EGR operation

Here's another approach for T6 DIY enthusiasts - taking advantage of very popular Carista OBDII-reader device - combined with an Android app. Ingredients: T6 EU6 engne: CXEB,CXEC,CXFA,CXGA,CXGB,CXGC,CXHA,CXHB. Carista OBDII device (also other generic OBDII (ELM327) devices will work) Android...

www.t6forum.com

 

[Ed_T]

Post-test drive follow up. NOx readings kicked in once the engine was up to temperature (after 10-15 mins). It tends to sit around <10 when bimbling along, temporarily increasing up to 200-250 when I floor it. From what I have read online, these are normal levels and suggests that the sensor is working (or at least it was during the test drive).